There are many different types of disc dispensers available for dispensing sensitivity discs in a predetermined pattern onto the surface of a culture medium within a receiving dish. Certain types of structures are designed for dispensing a single disc at a time from a single cartridge and others dispense, for example, eight or 12 discs in a predetermined pattern. With the multi-disc dispensers there are separate disc containing cartridges for each position on the dispenser.
Certain types are rotational type of dispensing mechanisms where one portion of the dispenser rotates with respect to another in order to dispense the discs and others rely on a reciprocal vertical plunger type of arrangement which employs linkage to dispense a disc from each of the cartridges in the dispenser. In the majority of dispensers which have been used throughout the years, once the dispensers have moved a disc from a cartridge into alignment with a discharge port the disc is permitted to fall freely onto the culture medium. Whatever control is maintained over the disc in its free fall is determined by the diameter of the opening of the discharge port and the length of the surrounding port through which the disc freely falls. Another factor which determines control over the freely falling disc is the height of the bottom open end of the discharge port from the culture medium within the receiving dish.
Examples of dispensers which utilize the freely falling dispensing mechanism when dispensing a plurality of discs simultaneously in a predetermined pattern are disclosed in U.S. Pat. No. 3,394,846 to Carski et al and U.S. Pat. No. 3,300,087 to Kuypers. Various different approaches from the free fall method of dispensing have been attempted, the most significant of which for purposes of this invention is the system employed in the Darpentigny et al. U.S. Pat. No. 3,836,047.
The object in mind with all disc dispensers is to be able to provide a selected number of discs for a particular receiving dish and test to be accomplished therein in an accurate predetermined pattern. Of importance is reliability and versatility. It is important that the discs intended to be dispensed on a particular stroke be all dispensed in the most accurate and quick and efficient manner possible. The dispenser should be of the type which is reliable in the sense that repeated use for many times will result in the same accurate and complete dispensing of the desired number and pattern of discs. Naturally, cost is also significant and in this respect simplicity of structure is desirable as well as low cost in materials. It should also be kept in mind that the simpler the structure the greater the reliability particularly when dealing with a low cost mass produced device. Furthermore, the more versatile and dependable the structure, the more desirable it is to the field. Different types of antibiotic tests require a different number and arrangement of discs and which in virtually all cases often depend upon accuracy in placement upon the culture medium.